1. Field of the Invention
The present invention is related to a fluidic fuel control system and, more particularly, to a constant mass air-fuel ratio fluidic fuel-injection system for use with internal combustion engines.
2. Description of the Prior Art
The art of fluidics has long been recognized as a natural technology for the sensing, computing, and controlling functions with respect to fuel and air flow to internal combustion engines. Prior art fluidic fuel control systems have ranged from carburetor enhancement type systems through complete pulse-width modulated all fluidic type systems. The carburetor enhancement devices utilize fluid amplifiers to improve the carburetor operation by linearizing or enhancing weak venturi signals, as exemplified by U.S. Pat. Nos. 3,656,736; 3,406,951; and 3,477,699. Continuous fuel-injection systems in which the number and location of injection points are not fixed as in carburetion systems are exemplified by prior U.S. Pat. Nos. 3,389,894; 3,679,185; and 3,690,625. The latter type continuous fuel-injection systems are, however, quite similar to the carburetor, in that venturi vacuum (and manifold vacuum) determines the amount of fuel to be delivered in a continuous manner. Such fuel-injection systems experience several problems among which are the vaporization of fuel having high velocity in the power jets of the fluid amplifiers, noise, and inadequate scheduling accuracy. To obtain the desired air-fuel schedule, the fluid amplifier must have a square root singlesided transfer characteristic that results in a slight leaning of the fuel-air mixture in the mid-range region, which function is quite difficult to obtain fluidically.
Pulsed fuel-injection systems have also been proposed and are exemplified by prior U.S. Pat. Nos. 3,672,339; 3,687,121; and 3,718,151. In such pulse-width modulation systems, the pulse frequency is directly proportional to the engine speed and the pulse width (at constant pressure) is modulated to vary the fuel consumption.
An air-modulation system has also been proposed, as exemplified by my prior U.S. Pat. No. 3,771,504, in which the operator controls the fuel consumption directly, while a control system adjusts the air consumption in a prescheduled closed-loop system.
In many of the fuel management systems described above, it is desirable to maintain a constant mass air-fuel ratio. This is inherently difficult to achieve since the basic measurement of airflow is generally on a volumetric basis, which must then be compensated for air-density variations due to barometric pressure and ambient temperature. Accordingly, prior art systems which have attempted to maintain a constant mass air-fuel ratio have required rather complex apparatus including pressure sensors, temperature sensors, and computation functions to arrive at a mass airflow measurement.